#include <iostream>
#include <utility>
#include <map>
#include <unordered_map>

using namespace std;

 
class Value {
public: 
    Value(string a, string b):_a{ a }, _b{ b } {}
private:
    string _a{ 0 };
    string _b{ 0 };
};

int main(int argc, char const* argv[])
{
    std::map<int, Value> map;
    // piecewise_construct 用来构造一个pair
    map.emplace(std::piecewise_construct,
        std::forward_as_tuple(1),
        std::forward_as_tuple(string{ "1" }, string{ "2" }));

    return 0;
}
